Stone of the Week - Celestine or Celestite

This is one of my favorite minerals and I love to collect it so much, hardly a gem show passes that I don’t buy a new specimen of it each year! The official name of this mineral is celestine, however it is still commonly called celestite, and is named from the Greek word "cœlestis", meaning for celestial due to its pretty pale blue color. Celestine is made up of strontium sulfate, or SrSO4, and is similar enough to another mineral, barite (BaSO4), that these are sometimes misidentified. This mineral commonly forms in sedimentary environments.

The pretty blue celestine crystals are a favorite among collectors.


Celestine comes in a variety of colors, including colorless, white, yellow, orange, gray, green, brown, and pale blue. It is the pale blue that is most commonly sold both as specimens and as beads. The introduction of celestine in the jewelry market is fairly recent, and can make for some beautiful jewelry. However, care must be taken as it is a soft stone, and can more easily be scratched than harder minerals such as quartz. It is also very slightly soluble (dissolves) in water, so do not expose it to water or moisture for any extended period of time. It is also best not to expose it to the Sun for extended periods if you do not wish the colors to fade.


These blue celestine crystals occur with white aragonite and a few purple fluorite crystals.


The worlds largest geode, located at Crystal Cave, Ohio (refer to previous article on geodes), is made of celestine. It is 35 feet at its widest point, and has crystals as wide as 18 inches across, estimated to weigh 300 lbs. Also of interesting note, there is a micro-organism called Acantharea (radiolarian protozoans) which have skeletons of strontium sulfate (aka Celestine). Celestine has sometimes been mined as a source of strontium, but always in very small quantities.


Crystal Cave, the worlds largest geode, is made up of large celestine crystals.



If there's a stone you would like to know more about - drop me a line! Have a mystery stone? Feel free to post a comment about it, including a link to a picture, and it could be featured on this blog!


Celestine Facts:
Chemical composition: SrSO4
Color: colorless, white, yellow, orange, gray, green, brown, pale blue
Habit: prismatic and tabular, also massive and granular
Fracture: uneven
Cleavage: prismatic and basal
Luster: vitreous
Hardness: 3-3.5
Specific Gravity: 3.9
Streak: White
Occurrence: Worldwide, mainly in the northern US, Europe, and Madagascar


References

Rocks, Minerals, & Fossils of the World by C. Pellant and R. Phillips. Published 1990 by Little, Brown and Co. ISBN: 0316697966

Mindat – Celestine. http://www.mindat.org/min-927.html

Wikipedia – Celestine. http://en.wikipedia.org/wiki/Celestine_(mineral)

Wikipedia – Crystal Cave. http://en.wikipedia.org/wiki/Crystal_Cave_%28Ohio%29

Stone of the Week - Copper

Copper is an elemental metal, represented as Cu on the periodic table. It is a very ductile metal, making it easy to shape and work with. Copper does not react with water (H2O), but does react to the oxygen in the air, forming a layer of brown-black copper oxide on copper metal. The green layer of copper carbonate (sometimes called a patina) that can form actually slows the corroding process. One of the most famous examples of this process is the green patina that has formed on the Statue of Liberty in the U.S. Copper can be found in mineral form as native copper, as well as in minerals such as chalcopyrite, azurite, malachite, and cuprite. Copper is very malleable as well as ductile, conducts heat well, and if near pure conducts electricity too.



Copper is mined and has a vareity of uses, particularly as jewelry components.



Due to the properties of Copper, it has a variety of uses, including copper pipes, copper wire, copper pans, and electronics. A special property of Copper is that it also can be used as an antibacterial and antifungal agent! Copper kills germs due to the toxic effect the metal ions has on bacteria, fungus, and mold spores. For this reason Copper has become more integrated particularly with hospital equipment. One example of this is brass doorknobs, which become disinfected within about eight hours or so.



This is what Copper looks like in a more 'raw' form as nuggets. Notice the green patina and the beginnings of oxidation occuring on the nugget to the left.



Copper exists in various locations through out the world, and has been used since ancient times. It has been in use for over 10,000 years, with the oldest known Copper pendant dating to 8700 BCE. Numerous artifacts comprised of Copper have been found world-wide, mainly as the alloy Bronze. Several copper alloys have been developed for different uses; common alloys with copper include bronze (copper and tin) and brass (copper and zinc). Today the world's largest mine for Copper is located at the Bingham Canyon Mine, located in Utah (U.S.), and is actually so large it is viewable from space!

Copper is a great alternative metal to use in jewelry work and is useful for practicing techniques as it is cheaper than Sterling Silver or Gold filled metal.

Copper has made a popular entrance into jewerly work recently as well. Although a slight greenish tint can occur when wearing Copper, numerous people have no reaction to it or don't wear the jewelry long enough for this to be a concern. Should this occur it can be easily washed off; additionally, some also try to coat the metal to protect both it and the person wearing it such as clear nail polish.

If there's a stone you would like to know more about - drop me a line! Have a mystery stone? Feel free to post a comment about it, including a link to a picture, and it could be featured on this blog!


Copper Facts:
Chemical composition: Cu, plus various alloy compounds
Color: Brown to coppery red
Habit: Branching and dendritic, can be massive
Fracture: Rough
Cleavage: None
Luster: Metallic
Hardness: 2.5-3
Specific Gravity: 8.9
Streak: Red-brown
Occurrence: Worldwide, some of the largest deposits in N. America and the UK

References
A Guide to Rocks and Fossils by B. Busbey III, R. R. Coenraads, P. Willis, and D. Roots. Published 2002 by Fog City Press. ISBN: 1877019518

Rocks, Minerals, & Fossils of the World by C. Pellant and R. Phillips. Published 1990 by Little, Brown and Co. ISBN: 0316697966

Wikipedia – Copper. http://en.wikipedia.org/wiki/Copper

Stone of the Week - Garnet

Garnets are actually a group of minerals, of which there are 15 different mineral species. Each mineral has a similar chemical make up -> X3 Z2 (SiO4)3 where X and Z can be different elements. It is these different combinations that make up the variation of minerals, although Calcium (Ca), Magnesium (Mg), Aluminum (Al), and Iron (Fe) are the most frequent. Out of the different minerals, there are several common garnets: pyrope (dark red), almandine (red to violet red), spessartite (yellow, rose, orange, reddish brown), grossular (white, yellow, yellow-green, brownish-red, orange, black), and andradite (colorless, yellow-green, brown, black). Within each of these are several varieties as well - hessonite and tsavorite are both types of grossular garnets for example.

This display at the National Museum of Natural History in the US shows some of the variety of color just within the grossular species.


Some of the most valuable garnets are also the rarest. Blue garnets are a type of pyrope garnet, that was discovered in the late 1990s in Bekily, Madagascar, and has since been found in the US, Russia and Turkey. It is one of the few garnet species that changes color from blue-green in the daylight to purple in incandescent light. Another sought after garnet is Tsavorite, which belongs to the grossular garnets, and is a brilliant green color. Tsavorite garnets were first discovered in a deposit in Tanzania during the 1960s, which extended into Kenya. The only other known location for these rare garnets is in Madagascar. Uvarovite is another bright green garnet that is one of the less common species, and is found in Russian and Finland.


Uvarovite is a spectacular green garnet, and is often sought after for jewelry.

Garnets are common world wide, particularly in metamorphic rocks such as marble and schist; pyrope garnets are usually associated with igneous rocks. They are abundant in the US, Brazil, South Africa, England, and Australia. Gemstone quality crystals are used in jewelry work, the most common being the red garnets. It is also the birthstone for January. Garnets have also been used as an abrasive for sand blasting, in cutting, and as part of some water filtration units.

Garnets can be found in nice crystal forms, such as the grossular garnets on the left. However the deep reds are a popular color found in jewelry.

If there's a stone you would like to know more about - drop me a line! Have a mystery stone? Feel free to post a comment about it, including a link to a picture, and it could be featured on this blog!



Garnet Facts:
Chemical composition: X3 Z2 (SiO4)3
Crystal System: Isometric/Cubic
Color: Varied – red, green, yellow, brown, black, blue, orange, clear
Habit: Well formed crystals are common, as well as massive and granular.
Fracture: Conchoidal
Cleavage: Indistinct
Luster: Vitreous, Resinous
Hardness: 6.5-7.5
Specific Gravity: 3.4-4.6
Streak: Colorless/White
Occurrence: Worldwide


References
A Guide to Rocks and Fossils by B. Busbey III, R. R. Coenraads, P. Willis, and D. Roots. Published 2002 by Fog City Press. ISBN: 1877019518

Rocks, Minerals, & Fossils of the World by C. Pellant and R. Phillips. Published 1990 by Little, Brown and Co. ISBN: 0316697966

Wikipedia – Garnet. http://en.wikipedia.org/wiki/Garnet

Adventures in Geology - Cedar Sink, KY

So my first field trip this semester was last week to a place called Cedar Sink, Kentucky. This was part of a lab out in the field for my geomorphology class. Geomorphology in general is the study of landforms - including classifying them, what processes form them, and sometimes the interactions between them and humans (how geomorphology can affect us, as well as how we affect the landscape).

Cedar Sink from an overview point.

Cedar Sink is located in south central Kentucky, inside the Mammoth Cave National Park, which is also the location of the largest known cave in the world, Mammoth Cave. Cedar Sink is aptly named because it is a collapse structure – also called sink holes or sinks. That is because this region is karst terrain, where the landscape is influenced by the dissolution of rock (essentially dissolves). When the rock is dissolved it can result in the formation of caves, as well as a variety of other features including sinkholes which are depressions in the ground formed by the removal of soil or rock.

A view of some of cave areas and one of the sinkholes filled with water. Blue arrow is pointing toward my professor to give an idea of the scale.

However, we weren’t there to study the sinkholes, but rather the hill slopes. The main point of our lab was to do sketches or profiles of the hill slopes. We also tried to determine what processes created them, as well as any that are resulting in the removal of the material on the hill slopes. These kinds of processes are important to understand, as they affect other processes such as groundwater movement, and can have an impact on human activity as in the case of land slides and rock falls.

Another side of the area that leads into a cave. As you can see from the ice cicles it was very cold that day!